A typical broadband power amplifier may include a radio frequency (RF) directional coupler. For example, a typical broadband power amplifier may be a multi-octave power amplifier that generally needs a broadband, multi-octave RF directional coupler for transmitter gain control (TGC). The broadband, multi-octave RF directional coupler may also be needed for voltage standing wave ratio (VSWR) detection, and receive (RX) protect detection. For example, a power amplifier covering a frequency range of about 225-2000 MHz covers operating bands where both very high frequency (VHF) and microwave design techniques may be used. However, neither a VHF nor a microwave approach may be sufficient for the overall desired operating band.
For example, a prior art system, as illustrated in FIG. 1, includes a toroidal directional coupler including two coupled toroidal transformers 13a, 13b. The toroidal directional coupler includes an input port 16a, and an output port 16b. The toroidal directional coupler also includes a forward coupled power port 17a, and a reflected coupled power port 17b. A power amplifier 11 is coupled to the toroidal directional coupler input port 16a, and an antenna 14 is coupled to the toroidal directional coupler output port 16b. Respective attenuators 15a, 15b are coupled to the forward and reflected coupled ports 17a, 17b. Respective detectors 12a, 12b are coupled to the attenuators 15a, 15b. 
The prior art system 10 generally requires, for a particular application, about a −35 dB coupling, and a flat response across the frequency range of 225-2000 MHz. The coupling is determined by the maximum output power of the power amplifier 11, a response of the detectors 12a, 12b, and the dynamic range of the system 10. However, the toroidal directional couplers 13a, 13b may perform poorly above 1.5 GHz, but provide improved bandwidth at lower frequencies. While toroidal couplers are typically used to achieve a bandwidth greater than one octave, using a toroidal coupler may cause problems above 1.5 GHz, as the loss is relatively high and directivity is relatively low.
In contrast, transmission line (stripline, microstrip, suspended stripline, etc.) couplers may have improved operation in the GHz frequencies, but may become too large in size to use near lower frequencies, for example, 225 MHz. However, unlike a toroidal coupler, a transmission line coupler is also typically limited to bandwidths of about one octave.
A transmission line coupler, for example, a stripline coupler, would be commonly used for applications above 800 MHz covering relatively narrow bands. However, a stripline coupler that spans 225-2000 MHz would have an increased overall size, which may make it increasingly difficult for a reduced size application, for example, in portable applications.
A combination of a transmission line and a toroidal directional coupler could be used to cover this band, but using both a transmission line and a toroidal directional coupler would require twice the board space, twice the detectors, twice the peripheral circuitry, and incur more insertion loss. Additional switches and logic would also be required.